The present invention relates to ultraviolet light curable compositions that may be utilized to produce a decorative metallic coating on a substrate.
UV radiation curable paint compositions are applied to a substrate through spraying, screen printing, dipping or brushing for the protection or decoration of the substrate. In the usual application, a substrate such as metals, glass, or plastics is coated with the paint composition and then UV light is introduced to complete the curing process. The UV curable paint compositions offer many advantages over typical heat curable compositions.
Heat curable compositions require the use of organic solvents that contain a significant amount of volatile organic compounds (VOCs). These VOCs escape into the atmosphere while the heat curable composition dries. Such solvent based systems are undesirable because of the hazards and expenses associated with VOCs. The hazards include water and air pollution and the expenses include the cost of complying with strict government regulation on solvent emission levels. In contrast, UV curable compositions contain reactive monomers instead of solvents; thus eliminating the detrimental effects of the VOCs.
The use of heat curable compositions not only raises environmental concerns but other disadvantages exist with their use as well. Heat curable compositions suffer from slow cure times which lead to decreased productivity. These compositions require high energy for curing due to energy loss as well as the energy required to heat the substrate. Additionally, many heat curable compositions yield poor film properties that result in decreased value of the end product.
Although UV curable compositions exhibit superior properties and performance over their heat curable counterparts, UV curable compositions themselves suffer from certain disadvantages. Generally, UV compositions have high molecular weights and a substantial degree of cross linkage due to the highly reactive nature of the composition. As a result, many of these compositions suffer from low durability and resin shrinkage. With the use of many such compositions, an inordinately high amount of UV light is required to cure. New formulations that lessen these problems typically suffer from diminished abrasion, chemical, and scratch resistance as well as low thermal stability and adhesion.
An addition disadvantage of typical UV compositions is their lack of stability which results in dispersion. With some compositions, suspended solids fall out of solution after a period of one to two days. Dispersion adversely affects the gloss and clarity of the finished product. To combat this problem, new compositions have been formulated with higher viscosities which often lessen the flowability of the composition. These viscous formulations rule out spray application and provide for an unsuitably high dipping thickness.
Accordingly, there exists a need to provide environmentally safe UV curable paint compositions which exhibit improved weatherability, corrosion resistance and workability. Additionally, there is a need to provide a method of applying the composition which furthers the goal of improved performance.
It is an object of the present invention to provide an improved composition that upon curing by ultraviolet light produces a decorative metallic coating.
It is another object of the present invention to provide an improved decorative metallic composition that can be applied by spraying, screen printing, dipping, and brushing.
The present invention discloses an ultraviolet light curable decorative metallic composition and method for making such a composition that may be used to produce a decorative metallic layer. The disclosed composition does not contain any significant amount of volatile organic solvents that do not become incorporated in the active layer after curing. Specifically, the decorative metallic composition contains 5% or less volatile organic solvents by weight.
In accordance with one aspect of the invention, an ultraviolet light curable decorative metallic composition is provided. The decorative metallic composition comprises an acrylated epoxy oligomer in an amount of about 20% to 45%, an isobornyl acrylate monomer in an amount of about 15% to 40% of the decorative metallic composition, a photoinitiator in an amount of about 4% to 14% of the decorative metallic composition, a flow promoting agent in an amount of 0% to 8% of the decorative metallic composition, and a metallic pigment in an amount of 5% to 40%. All percentages of the decorative metallic composition as expressed in this document refer to the weight percentage of the stated component to the total weight of the decorative metallic composition in its fluid state at standard temperature and pressure.
In accordance with yet another aspect of the invention, a method is provided for depositing a decorative metallic coating on a substrate. The method comprises a first step of applying to the substrate a decorative metallic fluid-phase composition (xe2x80x9cdecorative metallic compositionxe2x80x9d). The decorative metallic composition includes an acrylated epoxy oligomer in an amount of about 20% to 45%, an isobornyl acrylate monomer in an amount of about 15% to 40% of the decorative metallic composition, a photoinitiator in an amount of about 4% to 14% of the decorative metallic composition, a flow promoting agent in an amount of 0% to 8% of the decorative metallic composition, and a metallic pigment in an amount of 5% to 40%.
The method also includes a second step of illuminating the decorative metallic composition on the substrate with an ultraviolet light to cause the decorative metallic composition to cure into the decorative metallic coating.
In accordance with this method, the decorative metallic composition can be selectively deposited on the substrate at specific locations where decorative metallic plating is desired. It need not be applied to the entire substrate.